When a projector is set up so that the optical axis is not perpendicular to the projection screen, keystone distortion occurs. This distortion can be one-dimensional (i.e., vertical or horizontal offset) or two-dimensional (i.e., vertical and horizontal offset). Keystone distortion occurs when the projected image plane is not parallel to the screen plane and the optical axis is not perpendicular to the screen plane. Although several keystone correction techniques are available for projector systems, various shortcoming and deficiencies continue to persist.